1. Field of the Invention
The present invention relates to an image input apparatus, such as a digital camera, to which an external recording medium is removably attachable, and a control method therefore.
2. Description of Related Art
In a conventional digital camera, an interface circuit such as a buffer is provided between a system bus and a socket for a memory card, as disclosed in Japanese Laid-Open Patent Application No. 2000-295508. The interface circuit is configured to connect the memory card to the system bus. The system bus is included in a control system to which a microprocessor and memories, such as a ROM and a RAM, are connected. The interface circuit is composed mainly of a bus transceiver and has the function of preventing noise from being transmitted to the system bus. This noise occurs when a power source for the memory card is turned off for the purpose of saving electric power or when operation modes of the memory card are changed or when the memory card is inserted or removed while being supplied with electric power.
However, since the interface circuit has various components, sufficient space for mounting these components is required. This causes an increase in size of the system and an increase in cost thereof.
Furthermore, in cases where, in the above-described digital camera, the control system is composed of one integrated circuit, an interface circuit is also required between the memory card and a system bus included in the integrated circuit in order to prevent the turning-off of the power source for the memory card or the insertion or extraction of the memory card with power supplied from affecting the system bus. This necessitates that the integrated circuit be provided with data bus pins for the memory card in addition to pins for devices such as a ROM. Therefore, the integrated circuit is required to have a large number of pins. As a result, the integrated circuit becomes larger, thereby causing an increase both in system size and in cost of the integrated circuit.
Japanese Laid-Open Patent Application No. Hei 10-97357 discloses a system for coping with this problem. In that technology, in a system in which a PC card (PCMCIA card) is used as the memory card, a data bus and an address bus for the PC card are coupled to a data bus and an address bus of the system together with a ROM, a RAM, etc. During a period of time when the state of card detection terminals of the PC card is changing, the operation of a CPU of the system is caused to temporarily stop. Accordingly, it is possible to eliminate the influence of noise caused by insertion or extraction of the PC card.
However, it is difficult to detect all of the noise caused by insertion or extraction of the memory card (PC card) by using the card detection terminals of the PC card. For example, if the power source terminals of the PC card have deteriorated, the PC card's power source may be shut off before the insertion or extraction of the PC card detection terminals is detected. In this case, the data bus level is made low by the PC card power shut off such that data output from a memory element is accidentally changed. In this instance, if the CPU is in the process of reading out instructions from the ROM, the instructions read out by the CPU may be erroneous thus resulting in a system crash (system hang up).